1. Field of the Invention
The present invention relates to a sensor structure, e.g., for a yaw rate sensor.
2. Description of the Related Art
Such sensor structures are generally known. For example, published German patent application document DE 10 2009 046 506 A1 discloses a yaw rate sensor with Coriolis elements for measuring a yaw rate extending parallel to a main extension plane of the sensor substrate. The sensor includes a first and a second Coriolis element, which are connected to each other via a rigid bar acting as a rocker and two springs and are excited into opposite-phase oscillations parallel and antiparallel to an oscillation axis extending parallel to the main extension plane. The Coriolis elements are also attached to the substrate through additional spring elements. In the presence of a yaw rate parallel to the main extension plane and perpendicular to the oscillation axis, Coriolis forces running perpendicularly to the main extension plane act on the first and the second Coriolis element, and deflect the first and the second Coriolis element perpendicular to the main extension plane.
The yaw rate sensor also has detection means in the form of surface electrodes between the substrate and the Coriolis elements. The surface electrodes overlap the Coriolis elements perpendicular to the main extension plane, forming with the Coriolis elements a plate-type capacitor structure, which permits capacitive measurement of the change in clearance between the Coriolis elements and the surface electrodes. The deflection of the two Coriolis elements is determined from the measurement of the change in clearance and from this the yaw rate is calculated by differentiation. In this process, using two separate seismic masses makes it possible to distinguish between the present yaw rate and the present acceleration, a shared oscillation frequency for the two seismic masses being achieved due to the coupling via the rocker, only one drive and detection circuit being needed. This is particularly important since such sensor structures are typically resonantly operated at the respective frequencies.
In addition to the desirable usable modes “drive mode” and “detection mode” there are respective undesirable parallel modes, the frequency range in the related art being only a little different from the desirable antiparallel usable modes. In particular, in the event of external excitation due to the resonance exaggeration, the parallel detection mode may result in large deflections and thus in an error signal. That is generally undesirable because of the sensitivity to interfering frequencies. Therefore, specific embodiments for the application are of interest, particularly in the automobile sector, in which the frequency range of the parallel mode is above the antiparallel usable mode as far as possible.